1. Field of the Invention
The present invention relates generally to the connection of line circuits of a digital time-multiplex telephone network, and more specifically to an interconnect circuit which provides an indication of line conditions.
2. Description of the Prior Art
It is known to be desirable to have a universally applicable interconnect circuit which, under differing line conditions also requires different types of indications of such conditions. Thus, it is desirable in such an interconnect circuit to present a subscriber line circuit loop/closure caused by an off-hook indication, as well as a ground potential indication within the scope of signaling between a local exchange and a branch exchange by the application of ground potential to one core conductor of a central office line at a particular switching circuit configuration at the central office. As far as a connection for a subscriber line for a dual service connection of an interconnect line is concerned, a corresponding indication of a subscriber off-hook condition is desirable.
There is an overriding requirement of a line indication of insensitivity to pick-up of alternating current noise voltages, especially network power line a.c. noise voltages.
With regard to the above known requirements, interconnect circuits have been developed in the prior art which provided separate indication circuits for loop closure indication, and for ground potential indication and/or indication of an off-hook condition produced by a subscriber of a dual service connection.